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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2751) Datanode drops OS cache behind reads even for short reads
Date Wed, 25 Jul 2012 07:45:38 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2751?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13422067#comment-13422067
] 

Tsz Wo (Nicholas), SZE commented on HDFS-2751:
----------------------------------------------

+1 the branch-1 patch looks good.
                
> Datanode drops OS cache behind reads even for short reads
> ---------------------------------------------------------
>
>                 Key: HDFS-2751
>                 URL: https://issues.apache.org/jira/browse/HDFS-2751
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node
>    Affects Versions: 0.23.0, 0.24.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: 0.24.0, 0.23.1
>
>         Attachments: HDFS-2751.branch-1.patch, hdfs-2751.txt, hdfs-2751.txt
>
>
> HDFS-2465 has some code which attempts to disable the "drop cache behind reads" functionality
when the reads are <256KB (eg HBase random access). But this check was missing in the {{close()}}
function, so it always drops cache behind reads regardless of the size of the read. This hurts
HBase random read performance when this patch is enabled.

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